Lately, a number of synthetic peptide substrates have been described. The majority of these present a tripeptide chain where either the amino group of the N-terminal amino acid is blocked by an acyl group or is free but then having the D-configuration. The C-terminal amino acid is blocked by a chromogenic or a fluorogenic group which is split off in the reaction of the enzyme with the substrate. The thus formed, liberated chromophoric or fluorescent group can be quantitatively determined by photometric or fluoroscence-photometric methods. The enzymatic activity can be calculated by measuring the amount of cleavage product liberated per time unit.